Angled cutoff in bottom of blow mold

ABSTRACT

Mold parts are closed about a preformed parison pinching it shut at one end preparatory to blow molding it to a hollow article. A cutoff blade slides within one mold part at an angle so as to enable it to sever the parison at a point adjacent the seal line of the article being formed. This arrangement allows pinching shut parisons made of crystalline materials such as 1-olefin polymers, which parisons have been heated to a temperature just below the crystalline melting point, in such a manner that a good seal is obtained with the seal line being in an indented portion of the bottom; thus the bottle will sit flat on a surface.

United States Patent Richard D. Johnston Blackfoot, Idaho Sept. 12, 1969Jan. 4, 1972 Phllllps Petroleum Company Inventor App]. No. FiledPatented Assignee ANGLED CUTOFF IN BOTTOM OF BLOW MOLD 4 Claims, 6Drawing Figs.

US. Cl 425/302, 425/289, 425/387, 425/395, 425/397 Int. Cl B29d 23/03Field of Search 18/5 BM, 5 Bl l, 5 BO, 5 BS References Cited UNITEDSTATES PATENTS 2,890,483 6/ 1959 Soubier 18/5 BS 3,449,792 6/1969Plummer 18/5 BH 3,457,590 7/1969 Dittmann 18/5 BQ FOREIGN PATENTS631,708 1962 Italy 18/5 BS Primary Examinerl-l. A. Kilby, .lr.AttorneyYoung and Quigg ABSTRACT: Mold parts are closed about apreformed parison pinching it shut at one end preparatory to blowmolding it to a hollow article. A cutoff blade slides within one moldpart at an angle so as to enable it to sever the parison at a pointadjacent the seal line of the article being formed. This ar- 1 rangementallows pinching shut parisons made of crystalline materials such as1-olefin polymers, which parisons have been heated to a temperature justbelow the crystalline melting point, in such a manner that a good sealis obtained with the seal line being in an indented portion of thebottom; thus the bottle will sit flat on a surface.

PATENIEll-Il 4W2 FIG.

FIG. 4

INVENTOR. R. D. JOHNSTON FIG.

A T TORNE VS ANGLED CUTOFF IN BOTTOM OF BLOW MOLD BACKGROUND OF THEINVENTION This invention relates to an improved method of sealing andsevering parisons of crystalline thermoplastic material preparatory toblow molding.

The most economical manner for forming parison preforms is tocontinuously extrude a length of tubing and cut it into individualpieces of the proper length. The stretching and forming operation musttake place at a temperature just below the crystalline melting point inorder to take advantage of the molecular orientation effect. Thus, ifthe advantages of molecular orientation are to be achieved along withthe advantages of producing the parisons by continuous extrusion oftubing, as opposed to injection molding a closed end parison, some meansmust be devised to effect a good seal of the parison at this temperaturewhich is below its crystalline melting point. Turner, U.S. Pat. No.3,390,426, discloses sealing such parisons by means of multiple pointedmembers moving radially toward a point with a tamping foot within theparison which presses against the closed radial members. From thestandpoint of simplicity, the ideal arrangement would be simply to closea mold on the parison with a configuration at the bottom of the moldwhich would seal and sever the parison in a manner similar to thatutilized in conventional blow molding. However, since the polymer is atsuch a low temperature that it will not flow, this does not yield asatisfactory seal.

SUMMARY OF THE INVENTION It is an object of this invention to provide animproved apparatus to seal an olefin polymer parison at orientationtemperature.

It is a further object of this invention to provide improved apparatusto form high strength clear hollow articles from 1- olefin polymers.

It is still a further object of this invention to provide for sealingand severing a crystalline thermoplastic parison at orientationtemperature while said parison is in a mold.

According to this invention, mold parts are clamped on atemperatureconditioned parison to seal the walls of said parisontogether at a bottom end of said mold, said thus sealedoff endthereafter being severed from the remainder of said parison by a cutoffmeans in said bottom of said mold, said cutoff means traveling at anangle to a bottom wallforming surface of said mold.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings, forming a parthereof, wherein like reference characters denote like parts in thevarious views,

FIG. 1 is a schematic view of a complete blow molding ap? paratusutilizing the angled cutoff of the instant invention;

FIG. 2 is a crosssectional view of the mold parts with the parison heldin the clamping means;

FIG. 3 is a view similar to FIG. 2 in a later stage of the operation;

FIG. 4 is a detailed view of the bottom portion of the mold P FIG. 5 isa perspective view of a bottle molded in accordance with the instantinvention; and

FIG. 6 is a perspective view of the cutoff member as seen from the top.

DESCRIPTION OF THE PREFERREDEMBODIMENTS strengthening occurs onstretching. Examples of suitable resins include polymers and copolymersof monol-olel'ms having two to eight carbon atoms and the like.Preferred materials are polymers and copolymers of ethylene, propylene,and lbutene, with polypropylene being especially preferred.

These polymers are extruded or molded into parison preforms and thencooled to a temperature below their crystalline freezing point. Theparisons are then heated to an orientation temperature which isgenerally about l50 F., preferably 2-20F., below their crystallinemelting temperature. The crystalline melting point can be determined byheating a sample of the material under a polarizing microscope. Thespecimen is heated slowly and the point at which the last birefringencedisappears is the crystalline melting point.

Following conventional technology, reference to crystalline" polymersmeans solid polymers normally having a high degree of crystallinity,that is, at least 50 percent, as determined by X- ray analysis orcomparable methods.

In accordance with this invention, the parison walls are sealed by meansof pressing them together from the side by the bottom portions of themold halves as they close. After the walls of the parison have beenpressed together to form a seal, a severing means slides at an anglethrough one of the mold halves to sever the parison, leaving a small tabof the sealedtogether parison attached to the article. By having thecutoff mechanism slide at an angle, the mold can be so contoured as toform a recess in the bottom of the bottle so that the tab can projectdownwardly and yet not interfere with the bottle sitting level on a flatsurface.

Referring now to FIG. 1, there is shown a blow molding apparatuscomprising a frame 10. Supported by the frame is an oven 12. Parisons 14are conveyed through this oven by means of a continuous chain 16carrying support pins 18. Heated parisons 14 are lifted off of supportpins 18 by means of a transfer mechanism comprising a pivotal andlaterally reciprocal arm 20. The parisons are grasped by arm 20 at thebottom end thereof, lifted upwardly over the support pin, transferredlaterally to a position under thread-forming jaw 22, and then movedupwardly by means of the extension of cylinder 24, which carriestransfer arm 20. The upper end of parison 14 is thereby positionedwithin threadforming jaw 22, and this jaw then closes about said parisonto clamp it securely and in so doing, to form the threads in the case ofa bottle. Transfer arm 20 is then withdrawn and the bottom end ofparison 14 grasped by means of gripping elements 26 which are alsocarried by frame 10.

Gripping elements 26 hold the bottom end of parison l4 securely asthreadforming jaw 22 raises to thereby stretch and molecularly orientparison 14 in a longitudinal direction. Threadforming jaw 22 retracts toa position flush with the inner surface of the articleforming cavity,formed by mold halves 28 and 30, as shown in FIG. 3. Mold halves 28 and30 have inserts 32 and 33 designed to form a recess in the bottom of thearticle being molded. As can be seen from a view of FIGS. 3 and 4, asthe mold halves close, the parison wall is pinched flat and squeezedsecurely together by means of inserts 32 and 33.

After the parison walls have been forced together under pressure toeffect a seal, cutoff member 34 slides at an angle through mold half 30and insert 32 to sever the portion of the parison forming article 36from the scrap portion 38 as shown in FIG. 4. Cutoff member 34 is agenerally flat bladelike member with a pointed edge which abuts againstthe insert member 33 carried by the opposite mold half. It is held in aretracted position by spring 40 and is forced forward by means of aircylinder 42. In FIG. 4, obviously, the process is shown at a later stagefrom that of FIG. 3, at which later stage the parison has been blown outinto conformity with the mold walls. Cutoff member 34 may be actuatedany time after inserts 32 have pressed the walls of the parison togetherto effect a seal. That is, it may be actuated before the blow pressurehas been introduced into the parison, or after the blow pressure hasbeen introduced. In either event, the inserts 32 and 33 form a recess inthe bottom of the container so that the small tab 44 will not precludethe article from sitting flat on a level surface.

Cutoff member 34 contacts the portion of mold half 28 represented byinsert 33 at a point spaced downwardly from bottom forming surface 45 adistance of from l/l to onehalf inch, preferably l/64 to l/l6 inch, tothus form a tab of corresponding length.

Gripping elements 26 can be retracted if desired after the mold closes.Particularly in an alternate embodiment such as is shown in FIG. 3 wherea tamping foot 43 presses against the seal from the inside, this may benecessary to allow some movement of the tail portion as the cutoffmember 34 severs the flattened portion of the parison. Cutoff member 34may completely sever the tail from the remainder of the parison so thatit falls free on opening the mold, or a thin web may connect it to thearticle which has been molded; this web can be easily broken, forinstance, by leaving the gripping elements 26 engaged and moving themrelative to the article.

FIG. shows a perspective view of the bottom of a bottle formed using theinstant invention. Within recess 46 of the resulting container, whichrecess is formed by inserts 32 and 33, there is shown tab 44. Slidingcutofi member 34 is of a width essentially equal to the length of tab44.

It is essential that sliding cutoff member 34 be positioned at an angleso as to allow the cutting operation to take place in a recessed area;otherwise, the parison would have to be severed exactly flush with thebottom surface of the article, which would be difficult to do and whichwould result in a weak seal with the type of polymer in question, thatis, a crystalline polymer at a temperature below its crystalline meltingpoint.

It is further essential that the cutoff member 34 be actuated to severthe parison at a time after the molds have closed and sealed the parisontogether by the action of inserts 32 pressing the walls tightlytogether. If the cutoff member 34 were extended as the mold closes so asto sever the parison as it is being sealed, the portion of the parisonforming tab 44 would not be pressed together as securely, and therefore,an inferior seal would result. Here again is a step which is criticalbecause of the type of material being sealed. In an ordinary blowmolding operation involving a molten or tacky parison, the sealing andsevering could occur simultaneously and there could be great leeway inthe configuration of the sealing and severing surfaces without affectingthe quality of the seal.

It is noted that in this process just described, the mold closes on aportion of the parison which has been stretched. The combination ofhaving the parison stretched prior to closing the mold to seal andactivating cutofi member 34 after the walls have been scaled togetherthat provides an exceptional seal. In this regard, it is noted thatwhile the drawings show the stretching occurring by moving thethreadforming head upward, it is equally feasible to have thethreadforming head at the top of the mold initially and to stretch theparison by bringing the means holding the bottom downward. Also, theentire operation could be disposed upside down to that shown, or even ina horizontal plane.

In embodiments where the cutoff member 34 is actuated before the parisonis blown out against the mold walls, the parison is prevented fromretracting by virtue of tab 44 being held between inserts 32 and 33,thus eliminating the need for a tamping foot for this purpose.

Many standard parts such as temperature controllers, relays, fittings,and the like have not been shown in the drawings for the sake ofsimplicity, but their inclusion is understood by those skilled in theart and is within the scope of the invention.

EXAMPLE I Propylene homopolymer having a density of 0.905 (ASTM D1505-63T), a melt flow of 2 (ASTM D 1238-62T, Condition L), nd acrystalline meltin point of 340F. was extruded into tubing having aninternal rameter of 0.8 mch and a wall thickness of 0.125 inch. Thetubing was cooled to room temperature and cut into 7-inch lengths. These7- inch lengths were heated to a temperature of 320 -338 "F., grasped ata top end by a threadforming means such as means 22 shown in thedrawings and at the bottom end by a gripping element such as element 26shown in the drawings. The parison was then stretched by moving thethreadforming head upward as shown in FIG. 3 of the drawings. Moldsections were then closed as shown in FIG. 3 of the drawings to pinchthe parison shut and seal the walls along the bottom of the mold. Afterthe mold halves were completely closed, sealing the walls of the parisonshut along a flattened area, a flat blade moving within the mold wall asshown in the FIGURES was actuated to sever the parison so as to separatethe body portion from the tail. Thereafter the blow air was introducedto form the parison against the mold walls thus effectingcircumferential molecular orientation as is shown in FIG. 4. The moldswere opened and the resulting 28- ounce bottle removed. The bottle had atab such as tab 44 shown in the drawing depending from the bottomsurface of the recessed portion of the bottom about 1/32 of an inch.This bottle was found to have a watertight seal.

EXAMPLE II A number of bottles were made exactly in accordance with thedescription of example I and tested for a watertight seal. One hundredpercent of the bottles were found to have a watertight seal.

While this invention has been described in detail for the purpose ofillustration, it is not to be construed as limited thereby, but isintended to cover all changes and modifications within the spirit andscope thereof.

lclaim:

1. Apparatus for forming hollow articles comprising in combination:

1.jaw means adapted to clamp a first end of a parison;

2. parison gripping means spaced apart from said jaw means, saidgripping means being adapted to grip a second end of said parison;

3. means to move said jaw means relative to said gripping means so as tostretch said parison;

4. at least two mold parts adapted to close about said parison, saidmold parts projecting inwardly relative to the interior of said moldparts at the bottom portion thereof in an area where said mold partscome together so as to form a recess in a bottom wall of a resultingarticle;

5. a cutoff member sliding at an angle through said inwardly projectingportion of one mold part, said sliding cutoff member being so disposedas to abut against the opposite mold member at a point spaced down froma bottom forming surface thereof a distance of l/ to onehalf of an inch;and

6. means to actuate said sliding cutoff member.

2. Apparatus according to claim 1 wherein said sliding cutofi meanscontacts said opposite wall at a point within the range of H64 to l/l6of an inch below said surface.

3. Apparatus according to claim 1 wherein said sliding cutoff member isa flat blade having a sharp cutting edge.

4. Apparatus according to claim 1 comprising in addition: means to heatsaid parison and means to transfer said parison from said heating meansto said jaw means.

1. Apparatus for forming hollow articles comprising in combination: 1.jaw means adapted to clamp a first end of a parison;
 2. parison grippingmeans spaced apart from said jaw means, said gripping means beingadapted to grip a second end of said parison;
 3. means to move said jawmeans relative to said gripping means so as to stretch said parison; 4.at least two mold parts adapted to close about said parison, said moldparts projecting inwardly relative to the interior of said mold parts atthe bottom portion thereof in an area where said mold parts cometogether so as to form a recess in a bottom wall of a resulting article;5. a cutoff member sliding at an angle through said inwardly projectingportion of one mold part, said sliding cutoff member being so disposedas to abut against the opposite mold member at a point spaced down froma bottom forming surface thereof a distance of 1/100 to 1/2 of an inch;and
 6. means to actuate said sliding cutoff member.
 2. Apparatusaccording to claim 1 wherein said sliding cutoff means contacts saidopposite wall at a point within the range of 1/64 to 1/16 of an inchbelow said surface.
 2. parison gripping means spaced apart from said jawmeans, said gripping means being adapted to grip a second end of saidparison;
 3. means to move said jaw means relative to said gripping meansso as to stretch said parison;
 3. Apparatus according to claim 1 whereinsaid sliding cutoff member is a flat blade having a sharp cutting edge.4. Apparatus according to claim 1 comprising in addition: means to heatsaid parison and means to transfer said parison from said heating meansto said jaw means.
 4. at least two mold parts adapted to close aboutsaid parison, said mold parts projecting inwardly relative to theinterior of said mold parts at the bottom portion thereof in an areawhere said mold parts come together so as to form a recess in a bottomwall of a resulting article;
 5. a cutoff member sliding at an anglethrough said inwardly projecting portion of one mold part, said slidingcutoff member being so disposed as to abut against the opposite moldmember at a point spaced down from a bottom forming surface thereof adistance of 1/100 to 1/2 of an inch; and
 6. means to actuate saidsliding cutoff member.